Has nothing to do with the computer, if the modem’s receive has a steady flash it is scanning for the downstream frequency. If you put the modem on the first cable line coming in and its the same thing, there is not a fuggin’ thing you can do until a tech comes out.
Since you were online at a point though, it probably means your receive signal is right at the edge and will be a shitty connection until a tech fixes it.
You can goto http://192.168.100.1 and the modem will tell ya what its failing at.